Method and apparatus for making drive screws



March 8, 1966 1.. J. LOVISEK 3,238,542

METHOD AND APPARATUS FOR MAKING DRIVE SCREWS Filed June 24, 1964 2 Sheets-Sheet J.

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March 8, 1966 L. J. LOVISEK 3,238,542

METHOD AND APPARATUS FOR MAKING DRIVE SCREWS Filed June 24, 1964 2 Sheets-Sheet z X /;z:z;;///2 Fig.6

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United States Patent 3,238,542 METHOD AND APPARATUS FOR MAKING DRIVE SCREWS Louis I. Lovisek, Cheshire, Conn., assignor to Screw 8:

Bolt Corporation of America, Pittsburgh, Pa., a corporation of Pennsylvania Filed June 24, 1964, Ser. No. 377,650 9 Claims. (Cl. 10-46) This invention relates to drive screws, and more particularly to an improved way of making them.

A drive screw is one provided with a plurality of threads that have such a pitch that the screw will be rotated by them when it is driven into an object by being struck on the head. Usually, the helix angle of the threads is between about 45 and 65. The screw cannot loosen without turning, and the friction between the screw and the surrounding object is generally too great for that. The usual way of making drive screws is to roll the threads into the shanks in one machine and form the heads in an entirely different machine. When the screws are to be very short, it is diificult to feed them into the thread-rolling machine.

It is an object of this invention to provide a method and apparatus for making drive screws in a faster, simpler and less expensive manner than heretofore. Another object is to provide a drive screw with greater holding power than conventional drive screws.

in accordance with this invention, the major portion of a cylindrical metal blank is forced lengthwise into a die cavity having helical grooves in its side wall. The blank is larger in diameter than the minimum diameter of the cavity, whereby portions of the blank are forced out into the groove to form drive threads. After the threads have been formed, the end of the blank that remains projecting from the die cavity is upset to form a head, following which the screw is ejected from the cavity. The blank may be forced into the cavity by means of a pin sliding in a passage containing the blank in front of the die cavity.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which FIG. 1 is a fragmentary section through drive screw forming apparatus showing a blank about to be pushed into a die cavity;

FIG. '2 is an enlarged view of the outer end of the die cavity;

FIGS. 3, 4 and are views similar to FIG. 1, but showing the different parts of the apparatus at different times during the making of a drive screw;

FIG. 6 is a sectional view showing the head-upsetting operation;

FIG. 7 is an enlarged view of the finished drive screw; and

FIG. 8 is an end view thereof.

Referring to FIG. 1 of the drawings, a die 1 is rigidly mounted in a suitable stationary support 2. The front end of the die is provided with a cavity 3 of generally cylindrical shape although the major portion of its side wall is provided with helical grooves 4 of a size, length and pitch to form the desired threads 5 on a drive screw (FIGS. 7 and 8). The inner ends of the grooves terminate short of the inner end of the cavity to leave an inner end portion 6 with an unbroken cylindrical side wall. The inner end wall of the cavity is formed by the inner end of a rod 7 slidably mounted in a bore '8 extending forward through the die from its back to the cavity. The length of cavity 3, and therefore the length of its end portion 6, can be varied if rod 7 is made adjustable along bore 8 by any suitable means.

In front of the die there is a die block 10 that is movable in any well-konwn manner toward and away 3,238,542 Patented Mar. 8, 1966 ice from the stationary die. It should be noted at this point that it is immaterial as far as this invention is concerned whether the die or the die block is movable relative to the other or whether both can be moved toward and away from each other. The die 1 is described as stationary merely for convenience. The die block is provided with a socket 11 facing the stationary die and containing a movable die 12 that is slidably mounted therein. The movable die is longer than the socket and normally projects a considerable distance from it because a coil spring 13 in the socket spaces the inner end of the die from a backing plate 14 mounted in stationary position in the inner end of the socket. The movable die and the plate have portions that project a short distance into the coil spring and that can engage flat against each other, if desired, when the spring is compressed.

The movable die is provided with an axial passage 16 through it that is in line with the die cavity. The diameter of the passage is slightly larger than the diameter of the cavity between its grooves, preferably also being slightly less than the cavity diameter at the grooves. The outer end portion of the pasasge flares forward to a diameter about the same as the maximum diameter of the die cavity. Slidably disposed in the inner end of the passage is a pin 17 that extends out of the die and has an inner end engaging or secured to backing plate 14. When the movable die is in its outer position there is enough space in its passage in front of the pin to receive a cylindrical metal blank 18, which fits the passage snugly and from which a drive screw is to be made. This blank is enough longer than the die cavity to provide sufiicient metal for making a drive head 19 (FIGS. 7 and 8).

After a blank has been inserted in the front end of the movable die 12, the die block is moved forward toward the stationary die to cause the movable die to engage the other around the die cavity as shown in FIG. 1. The blank will thus be lined up with the cavity. As the die block continues to move, pin 17 is moved forward through the now stationary movable die and pushes or forces the blank into the die cavity. This is facilitated by providing the outer end of the cavity with a slight flare. As the blank is pushed into the smaller cavity, some of the blank will be extruded out into the helical grooves to form threads around the blank as shown in FIG. 3. The mating threads and grooves will cause the blank to rotate in the cavity as the blank moves axially into it. By the time that the blank has reached the inner end of the threaded portion of the cavity, backing plate 14 will be closer to the movable die, as shown in FIG. 4. As this narrow space is reduced, the leading end of the blank will be forced into the ungrooved inner end 6 of the die cavity, where it will form a short cylindrical end 20 on the blank (FIGS. 5 to 8) against rod 7, which is held firmly in place by any suitable means, such as a member 21.

Since the blank is longer than the die cavity, an unthreaded portion of the blank remains in the front end of the movable die passage 16 after the die block has advanced as far as possible. The die block then is retracted, which first allows the spring 13 to expand and then withdraws the movable die from the end of the threaded blank projecting from the die cavity. As soon as this has happened, the die block is moved laterally across the blank until an upsetting die 23 mounted in the block is brought opposite the blank to position a concave recess 24 in the outer end of the die in line with the blank. As shown in FIG. 6, the die block is then moved toward the stationary die again to cause the upsetting die to upset the projecting portion of the blank and form it into the rounded head 19. This completes the making of the screw. Now the die blockis retracted again and then rod 7 is moved forward to eject the finished screw from the die cavity. This can be done by any suitable means actuating member 21. Of course, as the screw is pushed out of the die cavity, the registering threads and grooves will cause the screw to rotate. The appearance of the finished screw is shown in FIGS. 7 and 8. Due to the fact that with this method a screw can be produced with a larger thread root than conventional drive screws, there will be greater engagement of the screw and the material it is holding, so the holding power of the screw is greater than heretofore.

Although only a single stationary die and a single movable die and punch or pin have been shown, it will be understood that multiple dies and punches can be used in a well-known manner.

According to the provisions of the patent statutes I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. The method of making a drive screw, comprising providing a die with a generally cylindrical cavity having helical drive screw thread forming grooves in its side wall, forcing lengthwise into one end of the die cavity the major portion of a cylindrical metal blank larger in diameter than the cavity between the grooves, whereby to extrude portions of the blank into said grooves to form threads, upsetting the end of the blank projecting from said end of the die cavity to form a drive screw head, and ejecting the screw from said end of the cavity.

2. The method of making a drive screw having threads at a helix angle between about 45 and 65, comprising providing a die with a generally cylindrical cavity having helical drive screw thread forming grooves in its side wall, forcing lengthwise into one end of the die cavity the major portion of a cylindrical metal blank having a diameter greater than the minimum diameter of the cavity but less than the maximum diameter of the cavity, whereby to extrude portions of the blank into said grooves to form threads, upsetting the end of the blank projecting from said end of the die cavity to form a drive screw head, and ejecting the screw from said end of the cavity.

3. The method of making a drive screw, comprising providing a die with a generally cylindrical cavity having helical drive screw thread forming grooves in its side wall extending inwardly from one end and terminating a short distance from the opposite end of the cavity, forcing lengthwise into said one endof the die cavity the major portion of a cylindrical metal blank larger in diameter than the ungrooved portion of the cavity, whereby to extrude portions of the, blank into said grooves and ungrooved portion to form threads and provide the leading end of the blank with a reduced short cylindrical end portion, upsetting the end of the blank projecting from said one end of the die cavity to form a drive screw head, and ejecting the screw from the cavity.

4. Drive screw making apparatus comprising a die provided with a generally cylindrical cavity having helical drive screw thread forming grooves in its side wall, means for forcing into one end of said cavity the major portion of a cylindrical metal blank having a diameter greater than the cavity between the grooves to extrude some of the blank into said grooves to form threads, means for upsetting the portion of the blank projecting from said end of the cavity to form a drive screw head, and means for ejecting the screw from said end of the die cavity.

5. Drive screw making apparatus according to claim 4, in which the inner ends of said grooves terminate short of the inner end of the die cavity.

6. Drive screw making apparatus comprising a die provided with a generally cylindrical cavity having helical drive screw thread forming grooves in its side wall, said grooves having a helix angle between about 45 and 65, means for forcing into one end of said cavity the major portion of a cylindrical metal blank having a diameter greater than the cavity between the grooves to extrude some of the blank into said grooves to form threads, means for upsetting the portion of the blank projecting from said end of the cavity to form a drive screw head, the die being provided with a bore extending therethrough in axial alignment with said cavity, a rod slidably disposed in said bore and projecting from its outer end, and means for moving the rod inwardly of the bore to push the drive screw out of the die cavity.

7. Drive screw making apparatus comprising a die provided with a generally cylindrical cavity having helical drive screw thread forming grooves in its side wall, a second die engageable with the other die around said cavity and provided with a passage there-through axially aligned with the cavity, said passage being larger in diameter than the cavity between the grooves and adapted to snugly slidably receive a cylindrical metal blank longer than said cavity, a pin slidably mounted in the end of said passage remote from the cavity, means for moving the pin forward in the passage to force the blank into the die cavity and cause some of it to extrude into said grooves to form threads, means for withdrawing the second die from the portion of the blank remaining outside of the die cavity, means for upsetting said projecting portion of the blank to form a drive screw head, and means for ejecting the screw from said end of the die cavity.

8. Drive screw making apparatus comprising a stationary die provided with a generally cylindrical cavity having helical drive screw thread forming grooves in its side wall, a die block movable toward and away from said cavity and provided with a socket facing the cavity, a movable die slidably mounted in said socket and projecting therefrom and adapted to be moved forward into engagement with the stationary die when the die block is moved toward the stationary die, a coil spring in said socket behind the movable die normally spacing it from the inner end of the socket, the movable die being provided with a passage therethrough axially aligned with the said cavity and having a larger diameter than the cavity between the grooves, said passage being adapted to snugly receive a cylindrical metal blank that is longer than said cavity, a pin slidably mounted in the inner end of said passage and engaging the inner end of said socket, whereby when the die block is moved toward the stationary die the movable die first will engage the stationary die and then said pin will force the blank forward into the die cavity and cause some of it to extrude into said grooves to form threads, the movable die being withdrawn from the portion of the blank remaining in said passage when the die block is retracted, means for upsetting the portion of the blank then projecting from the die cavity to form a drive screw head, and means for ejecting the screw from the die cavity.

9. Drive screw making apparatus according to claim 8, in which said die block is movable laterally of the die cavity, and in which said upsetting means is an upsetting die carried by the die block and movable into an operative position in front of the die cavity when the die block is moved laterally.

References Cited by the Examiner UNITED STATES PATENTS 1,069,659 8/1913 Ferry 10-27 1,418,186 5/1922 Howarth 10-54 2,251,201 7/1941 Purtell 10-27 2,309,053 1/1943 Farrell 10--27 ANDREW R. JUHASZ, Primary Examiner. 

4. DRIVE SCREW MAKING APPARATUS COMPRISING A DIE PROVIDED WITH A GENERALLY CYLINDRICAL CAVITY HAVING HELICAL DRIVE SCREW THREAD FORMING GROOVES IN ITS SIDE WALL, MEANS FOR FORCING INTO ONE END OF SAID CAVITY THE MAJOR PORTION OF A CYLINDRICAL METAL BLANK HAVING A DIAMETER GREATER THAN THE CAVITY BETWEEN THE GROOVES TO EXTRUDE SOME OF THE BLANK INTO SAID GROOVES TO FORM THREADS, MEANS FOR UPSETTING THE PORTION OF HE BLANK PROJECTING FROM SAID END OF THE CAVITY TO FORM A DRIVE SCREW HEAD, AND MEANS FOR EJECTING THE SCREW FROM SAID END OF THE DIE CAVITY. 